Alkylated aromatic amines, e.g., diarylamines, such as alkylated diphenylamine, are well known in the art to be effective stabilizers/antioxidants in a wide variety of organic materials, for example, polymeric substances such as natural or synthetic rubber, other elastomers and plastics, lubricating oils including e.g., mineral oil derived lubricants and synthetic lubricants, etc. In many these applications, light colored products which are liquid at room temperature are desirable for a number of practical reasons.
Alkylation of diarylamines, such as diphenylamine, with olefins in the presence of suitable alkylation catalysts is well known in the art. For example, U.S. Pat. No. 2,943,112 discloses a two-step process whereby alkylation of diphenylamine, in the presence of acid catalysts or clay catalysts, with relatively unreactive olefins, such as secondary alkenes, is followed by an alkylation reaction with more reactive olefins to scavenge the unreacted diphenylamine, with clay catalysts providing the desired light color. The reaction can be run in a closed reactor at elevated pressure.
U.S. Pat. No. 3,496,230 discloses the preparation of a mixture of 80% dinonydiphenylamine and 15% nonyldiphenylamine in the presence of Friedel-Crafts catalysts such as AlCl3 and ZnCl2, but mixtures contaminated by traces of chlorine, metal compounds and undesirable by-products, e.g. N-alkylated diphenylamines and diphenylamines alkylated in the 2- and 2′-positions, are obtained which are black in color and very viscous.
European Patent Application No. 387 979 discloses the reaction of diphenylamine with an eight-fold excess of tripropylene carried out in the presence of large quantities of acid-activated clays and under reflux conditions.
U.S. Pat. No. 4,824,601 discloses the use of acidic clay catalysts for the alkylation of diphenylamine to produce a light colored, liquid product by reacting certain molar ratios of reactants within specific temperature ranges for a time sufficient to ensure the alkylated product contains less than 25% dialkylated diphenylamine. The limit on the amount of dialkylated diphenylamine is disclosed as necessary to avoid the formation of crystallized, solid products.
U.S. Pat. Nos. 5,672,752 and 5,750,787 disclose processes for alkylating diphenylamine with linear alpha olefins and diisobutylene in the presence of a clay catalyst, which selectively result in a higher proportion of monoalkylated diphenylamine and a lower proportion of unsubstituted diphenylamine and/or disubstituted or polysubstituted diphenylamines. Conditions favoring mono-alkylation are disclosed. U.S. Pat. No. 6,204,412 discloses a method of alkylating diphenylamine to obtain a light colored, liquid product, which comprises a two-step method wherein, in the second step, a second olefin is added to the reaction mixture containing diphenylamine and diisobutylene (and/or an alpha-olefin of the disclosed formula) to scavenge or reduce the amount of unreacted diphenylamine in the product
U.S. Pat. No. 6,315,925 discloses a process comprising alkylating diphenylamine with an excess of nonene or a mixture of isomeric nonenes in the presence of from 2.0 to 25.0% by weight, based on diphenylamine, of an acidic clay in the absence of a free protonic acid, resulting in a mixture containing at least 68.0% dinonyldiphenylamine, from 20.0 to 30.0% nonyldiphenylamine, not more than 3.5% trinonyldiphenylamine; and not more than 1.0% diphenylamine.
U.S. Pat. No. 6,355,839 discloses a process for preparation of alkylated diphenylamine antioxidant which comprises alkylating diphenylamine with a polyisobutylene in the presence of a clay catalyst, wherein the polyisobutylene has an average molecular weight in the range of 120 to 600 and wherein the polyisobutylene contains at least 25% methylvinylidene isomer.
U.S. Pat. No. 8,828,916 discloses a process for preparing nonylated diphenylamines which improves nonenes usage by recycling and reusing stripped unreacted nonenes from an earlier process. The process comprises consecutive recycle of recovered nonenes is conducted at a sequential two step temperature reaction. The nonene alkylated diphenylamine product mixture is a useful antioxidant when added to a lubricating composition.
There is still a need however for a more efficient and less expensive process for alkylating aromatic amines that will provide a high quality product with low color in a controllable manner.
Fixed bed reactors for catalytic reactions are known. One advantage of fixed bed reactors over, e.g., standard reaction kettles, is that they are readily adapted to continuous processes which can be used to control contact times with the catalyst by varying feed rates. Another advantage is the excellent heat transfer and control capability. Conceptually simple, one rudimentary fixed bed reactor useful for the present catalytic alkylation is a tube or column with a porous support at one end for preventing flow through of catalyst. The catalyst is loaded into the tube or column and reactants are passed through. The rate at which the reactants progress through the catalyst determines the residence time.
Of course, the shape of the fixed bed reactor is not limited to the rudimentary device above and a variety of geometries and sizes are known. Multibed reactors comprising several fixed bed reactors, typically in parallel, are common. Multiple passes can be used in a process if desired and it is possible to arrange two or more reactors in series. When using more than one single tube or multibed reactor, each reactor can contain the same or different catalyst, be of equal or different volume, heated or cooled at the same or different temperatures. It is also possible for the reactant composition to be the same or different in different reactors, for example, additional amounts of an alkylating agent, or in some embodiments a different reactive species, may be fed into a downstream reactor along with the reaction mixture produced in a previous reactor,